The invention relates to a metering pump and in particular to a metering pump comprising a metering chamber having an inlet connected with a predelivery chamber and an outlet connected with a metering point.
A metering pump of this kind is known from the German utility model No. 77 33 135. In the known metering pumps which operate agains a counter pressure the entry of air or gas into the pump chamber results in a power reduction or even in a failure of the metering means operated by the pump. This effect occurs when the metering pump is put into service, the metering agent tank is exchanged and also when metering agents gas out. During the pressure stroke the gas is compressed in the pump chamber due to the counter pressure in the system and expands again during the suction stroke. This air cushion prevents the aspiration or displacement of the metering liquid. This effect occurs in particular in metering pumps with small stroke volume and high stroke frequency.
Conventional metering means such as piston diaphragm pumps are not suitable for metering aggressive media such as chlorine bleaching solution, since signs of wear appear very rapidly in particular in the piston packings and hence the service life of such pumps is rather short. Metering pumps suitable for aggressive media are known, but these pumps are not self-venting or self-bleeding, so that the venting or aeration must be performed by hand. This leads to an irregular pumping operation and interruptions.